/*
  console.log(1);
  setTimeout(function () {
    console.log(2)
  }, 0);
  new Promise(function (resolve) {
    console.log(3)
    resolve()
  }).then(function () {
    console.log(4)
  })
  console.log(5)

  事件轮询 event loop
  1 3 5 4 2
*/
